1. Field of Invention
This invention relates to test equipment for testing of printed circuit boards and, in particular, to the construction of a circuit card (commonly referred to as a switch card) and its interconnection to electrical contacts of the printed circuit board test equipment.
2. Background of the Invention
Printed circuit boards are tested for circuit continuity and component integrity by the use of automated circuit board test equipment. This equipment is typically quite complex as it must have test probes which can contact various test points on a printed circuit board which are generally closely spaced. Commonly, the test equipment is provided with a "bed of nails" in which a plurality of evenly spaced test probes are located at evenly spaced increments on a grid, typically separated by distances of 0.1 inch or less.
Advances in circuit board and electronic component technology have escalated the spacing demands placed on circuit board test equipment. The state of the art technology requires circuit board test equipment capable of accessing test points which are spaced apart by as slight as 0.05 inch, or less.
While test probes can be evenly distributed across an expanded test bed surface which typically spans from 12 to about 36 inches in each direction, difficulty is experienced in providing reliable interconnections of probes in highly populated test beds to the internal circuitry of the test equipment.
Some of the earliest test equipment employed spring biased test pins (probes) with tails terminated with wires using soldering, crimping or wire wrapping. These wires, which were generally 2 to 6 feet long, provided electrical connection to the test equipment circuitry. The assembly of these circuit board test equipment was laborious and the circuit board test equipment was prone to failure because of the many mechanical connections.
An approach which has been used in a number of commercial test equipment has been to provide a plurality of parallel, closely spaced conductor plates (switch cards) which are provided with some type of edge connector along one edge of the switch card for electrical connection to the probes of the test equipment test bed. These cards are placed in a stacked array, orthogonal to the test bed of the test equipment and are usually provided with electrical components in a plurality of switching circuits for each of the individual probes of the test equipment.
A recent innovation has been to provide a flexible circuit which is carried on the switch card, and wrapped over one edge of the card to permit a plurality of cards to be stacked in a parallel side-by-side array with their edges abutting the test probes. The test probes have tails which seat against contact pads of the flexible circuit. With repeated use, the tails of the probes wear the flexible circuit, destroying continuity.